Create a Google Calendar of NZ tides for a defined location. This python3 script parses tide data obtained as a .csv file from Land Information NZ

NZ_tide_cal.py

import csv
from datetime import datetime, timedelta

# Create a Google Calendar of NZ tides for a defined location
# This python3 script parses tide data obtained as a .csv file from Land Information NZ
# The data files are downloadable from: https://www.linz.govt.nz/sea/tides/tide-predictions
# The output .csv file(s) can be imported into a Google Calendar

# Script was used to create tides for 2022, 2023 & 2024 at Weiti River Entrance
# The public Google Calendar is named: NZ_Tides_Weiti
# If you use this script for another location, please make the calendar public and use the same naming convention,
#   such as: NZ_Tides_Wellington

# N.B. script may fail if the input .csv file is not coded UTF-8.  
# Open in Excel or Libreoffice Calc, choose UTF-8 coding, then save the file before running this script

# Request location, input & output file names in terminal:
tide_at = input("Name of tide location - e.g. 'Weiti River Entrance': ")
tide_file = input("Name of .csv file to process (include .csv suffix): ")
calendar_file = input("Provide a name for calendar data file (include .csv suffix): ")


# tide data parsing function
def make_tide(tdate, ttime, tval, tstr):
    # create a list, this function will replace the values
    the_tide = ['0_Subj', '1_stDate', '2_stTime', '3_enDate', '4_enTime', '5_Desc', '6_Weiti', 'PUBLIC']

    # Add 30 mins to tide time, to create end time for calendar entry (will span midnight, if a tide is after 23:30)
    time_begin = tdate + " " + ttime
    time_plus = datetime.strptime(time_begin, '%d/%m/%Y %H:%M') + timedelta(minutes=30)
    date_end = datetime.strftime(time_plus, '%d/%m/%Y')
    time_end = datetime.strftime(time_plus, '%H:%M')
    
    #convert all tide height values to 1 decimal point
    thgt = float(tval)
    tval = str(thgt)

    # Acknowledge data source in calendar entry description field
    data_source = 'Tide data provided by Land Information NZ: https://www.linz.govt.nz/sea/tides/tide-predictions'

    # replace the_tide list values
    the_tide[0] = tstr + tval + "m"  # e.g. High: 3.2m
    the_tide[1] = tdate
    the_tide[2] = ttime
    the_tide[3] = date_end
    the_tide[4] = time_end
    the_tide[5] = data_source
    the_tide[6] = tide_at
    return the_tide


# open input .csv file
with open(tide_file, 'r') as read_obj:
    # pass the file object to reader() to get the reader object
    csv_reader = csv.reader(read_obj)
    # Pass reader object to list() to get a list of tide data (by day)
    dayList = list(csv_reader)


# the output is a separate list for each tide: three or four per day/row
# create empty output list
tide_data = []

# iterate through rows in csv file that contain tide data (the first 3 rows don't)
i = 3
while i < len(dayList):
    day = dayList[i]

    # Set up the variables to pass to the make_tide function
    # 1: create the date value string from csv columns 0,2,3
    tDate = day[0] + "/" + day[2] + "/" + day[3]

    # 2: get tide heights (High or Low) to for calendar display
    tH1 = day[5]
    tH2 = day[7]
    if tH2 < tH1:
        hiLo = ['High: ', 'Low: ', 'High: ', 'Low: ']
    else:
        hiLo = ['Low: ', 'High: ', 'Low: ', 'High: ']

    # 3: determine if there are 3 or 4 tides in the day (if 3, doesn't process the empty 4th column)
    if not day[11]:
        nCol = 9
    else:
        nCol = 11

    # Iterate through tide columns in "day" and pass tide values to make_tide function
    x = 4  # start at 5th column in aRow, increment by 2
    y = 0  # Choose "High" or "Low" from hiLo list, to pass to Subject (tStr)
    while x < nCol:
        tStr = hiLo[y]
        tVal = day[x + 1]
        tTime = day[x]
        a_tide = make_tide(tDate, tTime, tVal, tStr)

        # debug check - disabled: 
        # print(atide)
        # Add returned atide to tide_data output list:
        tide_data.append(a_tide)
        
        # iterate tides in a row
        y += 1
        x += 2
    # iterate rows
    i += 1

# create an output file (with the input file name)
with open(calendar_file, 'w', encoding='UTF8', newline='') as f:

    # Header Row as required for Google Calendar upload
    header = ['Subject', 'Start Date', 'Start Time', 'End Date', 'End Time', 'Description', 'Location', 'Private']

    # populate output file with header and data rows
    writer = csv.writer(f)
    # write the header
    writer.writerow(header)
    # write tide data rows
    writer.writerows(tide_data)

# all done